1. Field of the Invention
This invention relates to rotary kilns in which gaseous reactions are carried out to form a solid product. The invention has particular relevance, although not exclusively, to rotary kilns used to manufacture uranium dioxide powder suitable for subsequent conversion to nuclear fuel pellets.
2. Discussion of Prior Art
In one known type of rotary kiln uranium hexafluoride vapour is fed with steam into an inlet end of the kiln. Reaction between the uranium hexafluoride and steam produces a solid intermediate product in the form of uranyl fluoride which passes into a heated rotating barrel by the aid of a scroll feed device. As the uranyl fluoride progresses along the barrel it reacts with a counterflowing stream of hydrogen and steam. This reduces the uranyl fluoride to a uranium dioxide powder which is discharged from the outlet end of the kiln.
Off gases produced by reactions in the kiln flow towards the inlet end and pass into a filter hopper arranged above the scroll feed device. Mounted on the top of the hopper are several filter assemblies which are used to extract solid particles from the reaction gases.
In use, a major portion of the uranyl fluoride particles circulate within the inlet region for a period of time during which particle can grow and agglomorate in a dendritic manner. Eventually, the particles become disentrained from the reaction gases and fall into the scroll feed device which transfers them into the kiln barrel.